scispace - formally typeset
Search or ask a question
Author

Wohan Cui

Bio: Wohan Cui is an academic researcher from Case Western Reserve University. The author has contributed to research in topics: Flame spread & Materials science. The author has an hindex of 2, co-authored 2 publications receiving 21 citations.

Papers
More filters
Journal ArticleDOI
TL;DR: In this article, an array of 10 1.5 cm-long 5 cm-wide filter papers is uniformly distributed on a vertical sample holder subjected to double-sided burn, and the distance between the samples was varied from 0 to 4 cm.

18 citations

Journal ArticleDOI
TL;DR: In this article, a series of microgravity experiments of concurrent-flow flame spread over samples of ultra-low area densities are conducted using NASA Glenn Research Center's Zero Gravity Research Facility (the 5.18 ǫ s drop tower).
Abstract: There are no existing experimental studies of flame spread rate trends for ultra-thin solid samples. Previous theory has predicted that for concurrent flame in kinetic regime, the flame spread rate decreases as the sample thickness decreases and there is a critical thickness below which burning is not possible. To test this hypothesis, a series of microgravity experiments of concurrent-flow flame spread over samples of ultra-low area densities are conducted using NASA Glenn Research Center’s Zero Gravity Research Facility (the 5.18 s drop tower). The tested samples are cellulose-based materials of various area densities, ranging from 0.2 mg/cm2 to 13 mg/cm2, as low as one order of magnitude less than those ever tested before. Each sample is 30 cm long by 5 cm wide and is burned in a low-speed concurrent air flow (5 to 30 cm/s). The results show that the concurrent flame spread rate is proportional to the flow velocity relative to the flame and is inversely proportional to the sample area density. A theoretical formulation, provided in this work, suggests that the flame length has a linear relationship with the relative flow speed and has no direct dependency on the sample area density. The experimental data supports this conclusion. From the images recorded in the experiments, a unique flame base tubular structure directed upstream away from the burnout zone is observed for thin samples. This structure is suspected to be due to flame stretching and localized blowoff caused by the oxidative pyrolysis Stefan flows at the sample burnout. This can be an indication that the chemical time becomes comparable to the flow time of the Stefan flow and the tested samples are approaching the kinetically-limited thickness. For the thinnest tested sample (0.2 mg/cm2), flames with concurrent and opposed dual natures are observed when the air flow rate is low (< 20 cm/s). At the lowest tested flow rate (5 cm/s), the flame spread rate exceeds the air flow rate and the flame transits to an opposed flame in the concurrent flow. The dual nature and flame transition are presented and discussed. This study provides detailed examination through high-resolution images of the transition between the concurrent to opposed flame spread modes.

17 citations

Journal ArticleDOI
TL;DR: An experimental apparatus and a standard operating procedure are developed to collect time-resolved data on the gas compositions and fire characteristics during and post-thermal runaway of lithium-ion battery (LIB) cells as discussed by the authors .
Abstract: An experimental apparatus and a standard operating procedure (SOP) are developed to collect time-resolved data on the gas compositions and fire characteristics during and post-thermal runaway of lithium-ion battery (LIB) cells. A 18650 cylindrical cell is conditioned to a desired state-of-charge (SOC; 30%, 50%, 75%, and 100%) before each experiment. The conditioned cell is forced into a thermal runaway by an electrical heating tape at a constant heating rate (10 °C/min) in an environmental chamber (volume: ~600 L). The chamber is connected to a Fourier transform infrared (FTIR) gas analyzer for real-time concentration measurements. Two camcorders are used to record major events, such as cell venting, thermal runaway, and the subsequent burning process. The conditions of the cell, such as surface temperature, mass loss, and voltage, are also recorded. With the data obtained, cell pseudo-properties, venting gas compositions, and venting mass rate can be deduced as functions of cell temperature and cell SOC. While the test procedure is developed for a single cylindrical cell, it can be readily extended to test different cell formats and study fire propagation between multiple cells. The collected experimental data can also be used for the development of numerical models for LIB fires.
Journal ArticleDOI
TL;DR: In this paper , a series of experiments are performed using a vertical array of thin discrete fuels separated by heat absorbing inert materials of different thicknesses, and an existing model for flame spread rate is updated by incorporating the heat absorbing effects of the gaps.
Abstract: Flame spread over discrete solid fuels has been of key research interest in the past few decades. Most studies considered an array of discrete fuels separated by air gaps or heat-insulating inert materials. The effects of heat loss due to the discrete configuration are not well understood. The present study aims to bridge this knowledge gap. A series of experiments are performed using a vertical array of thin discrete fuels separated by heat-absorbing inert materials of different thicknesses. For comparisons, experiments are also performed using discrete fuels separated by air gaps and using continuous fuel. The flame base spread rate is found to be generally higher in discrete fuel than in continuous fuel configurations, due to a reduced fuel load per unit length. It is also found that the air and inert gaps have opposite effects on the solid burning rates. The air gaps break the no-slip boundary, allowing the laterally entrained buoyancy flow (normal to the sample surface) to push the flame closer to the samples. This leads to an enhanced heat flux on the sample surface and an increased solid burning rate. On the other hand, the inert materials retain the flow boundary profile and act as a heat sink during flame spread, thereby reducing the solid burning rate. As the inert thickness increases, flame spread rate and solid burning rate decrease. Based on these observations, an existing model for flame spread rate is updated by incorporating the heat-absorbing effects of the gaps. The correlation is validated using the experimental data.

Cited by
More filters
Journal ArticleDOI
TL;DR: In this article, the authors revisited the problem of opposed fire spread under limited and excessive oxygen supply and reviewed various near-limit fire phenomena, as recently observed in flaming, smoldering, and glowing spread under various environment and fuel configurations.

40 citations

Journal ArticleDOI
01 Apr 2021-Fuel
TL;DR: In this paper, the combined effect of inclination angle and array fuel bed width on flame spread over discrete fuel arrays was investigated. But, the authors did not consider the effect of the angle of inclination on the upward flame spread.

18 citations

Journal ArticleDOI
TL;DR: In this article, an array of 10 1.5 cm-long 5 cm-wide filter papers is uniformly distributed on a vertical sample holder subjected to double-sided burn, and the distance between the samples was varied from 0 to 4 cm.

18 citations

Journal ArticleDOI
TL;DR: In this paper, a group of birch rods with different lengths (denoted by l within 60-100mm) and spacings (S, 1-9mm) were analyzed experimentally and theoretically.

17 citations